Broadband ultraviolet light sources are used for various applications in the semiconductor processing industry. These applications include wafer inspection systems and lithography systems. In both types of systems it is desirable for the light source to have a long useful lifetime, high brightness and a broad spectral range of emitted light. Currently plasma-based light sources are used in lithography and wafer inspection systems. Plasma-based light sources generally include an enclosure containing a cathode, an anode and a discharge gas, e.g., argon, xenon, or mercury vapor or some combination of these. A voltage between the cathode and anode maintains a plasma or electric arc.
Prior art plasma light sources suffer from a number of drawbacks when used in lithography and inspection systems. The first drawback, common to both types of systems is that plasma light sources based on mercury and/or argon and/or Xenon have a limited amount of emission in the deep UV. It would be desirable to increase the amount of emission at vacuum wavelengths below about 260 nanometers. Unfortunately, mercury emission tends to die off rapidly at below 260 nanometers. Another drawback that is particularly relevant to wafer inspection systems is that the discharge tends to rapidly degrade. Wafer inspection systems collect light from the plasma over a relatively narrow solid angle and therefore require tight confinement of the plasma arc between the cathode and anode. Unfortunately, as the source ages, the cathode tends to erode and/or become contaminated and the arc tends to spread.
Thus, there is a need in the art, for a broadband plasma light source that overcomes the above disadvantages.